Germ cells are essential for the maintenance of all sexually reproducing species. Many cellular and molecular aspects of germ cell behavior including their early development as primordial germ cells (PGCs) and their differentiation into sperm and egg are conserved throughout the animal kingdom. This proposal focuses on the analysis of PGC migration. In most organisms PGCs originate at one place of the early embryo and migrate through the embryos to reach the somatic part of the gonad, where they differentiate. This process is intricately regulated and failures in embryonic germ cell migration have been attributed to the origin of extragonadal germ cell tumors in humans. This proposal combines biochemical and genetic approaches with in vivo imaging analysis to understand how migratory cues are integrated overtime and space using Drosophila as a model. In vivo imaging will be used to follow the germ cell migratory path during their transepithelial migration through the posterior midgut and their subsequent homing towards the somatic gonad in wild type and mutants. The G protein coupled receptor (GPCR), Tre-1, will be analyzed with regard to its role in initiating the migratory program and in transepithelial migration. The molecular nature of attractant and repellant somatic guidance cues will be characterized by studying the function of the previously identified lipid phosphatase pathway that is controlled, by Wunen and Wunen2, two homologs of mammalian lipidphosphate phosphatase 3, and by analyzing the isoprenoid pathway, that is controlled by HMGCoA reductase. With a more detailed knowledge of the pathways involved, the interplay between GPCR and Wunen function in germ cells, and the integration of somatic signaling by the Wunen and HMGCoA reductase pathways in the soma will be addressed. The overall goals of this proposal are to connect the molecular network of germ cell migration with the cellular parameters of the developing embryo. Aspects of germ cell migratory behavior are shared with other solitary migrating cells, such as cell of the immune system and metastasizing cancer cells. Thus, the analysis of the genetically easily amenable fruit fly germ cell system is likely to reveal more general principles controlling cell migration.